In LTE (Long Term Evolution), when transmission of an uplink data signal is desired, a mobile station UE is configured to adopt any one of methods of: transmitting an SR (scheduling request signal) by using setup resources for an individual SR dedicated for the mobile station UE as shown in FIG. 6; and transmitting the SR by using an “RA (random access) procedure” as shown in FIG. 7.
Specifically, as shown in FIG. 8, when the mobile station UE detects generation of an uplink data signal to be transmitted in step S201, the mobile station UE determines that the SR is supposed to be transmitted in step S202, and determines whether or not the resources for an individual SR dedicated for the mobile station UE are set up in step S203.
If “yes,” the operation proceeds to step S204. If “no,” the operation proceeds to step S207.
In step S204, the mobile station UE determines whether or not it is possible to transmit the SR in the most recent subframe corresponding to the resources for an individual SR.
If “yes,” the operation proceeds to step S206. If “no,” the operation proceeds to step S205.
In step S205, the mobile station UE suspends the transmission of the SR in the subframe, and the operation returns to step S204.
In step S206, the mobile station UE transmits the SR in the subframe by using the resources for an individual SR.
In step S207, the mobile station UE transmits the SR by using the “RA procedure” (see FIG. 7).
Meanwhile, in LTE, the mobile station UE may adopt two states, namely, an “IDLE state” and an “RRC_Connected state.”
The “IDLE state” is a state where connection between networks (a core network and a radio access network) and the mobile station UE is not established (where individual resources for the mobile station UE are not set up either). The mobile station UE in the “IDLE state” first has to transition to the “RRC_Connected state” in order to start transmission and reception of data signals.
On the other hand, the “RRC_Connected state” is a state where the connection between the networks and the mobile station US is established. The mobile station UE in the “RRC_Connected state” can perform transmission and reception of data signals.
Generally, it is preferable that the mobile station UE not having any data signals to be transmitted or received transition to the “IDLE state” from the viewpoint of effective use of its battery and radio resources.
In the meantime, an occurrence frequency of intermittent data such as background traffics is increased nowadays due to diffusion of smartphones and tablet terminals. Such an increase causes frequent occurrence of transitions between the “IDLE state” and the “RRC_Connected state” as shown in FIG. 9, and leads to a problem of an increase in signaling load on the core network (CN).
Hence, a control method called an “always-on” method to keep the mobile station UE always in the “RRC_Connected state” is being studied (see FIG. 10). As shown in FIG. 10, the “always-on” method can suppress signaling involving the core network (CN) in association with the transitions of the mobile station UE between the “RRC_Connected state” and the “IDLE state.”
A problem of the “always-on” method is a potential shortage in individual resources to be allocated to each mobile station UE as a result of an increase in the number of mobile stations UE which are in the “RRC_Connected state” at the same time.
Here, the individual resources are thought to include “resources for a periodic SRS (sounding reference signal),” “resources for a PUCCH (physical uplink control channel)-CQI (channel quality indicator),” “resources for a PUCCH-SR (the resources for an individual SR),” and the like.
The “resources for a periodic SRS” are resources used by the mobile station UE for periodically transmitting an SRS used for AMC (adaptive modulation and coding) and the like of the mobile station UE.
Meanwhile, the “resources for a PUCCH-CQI” are resources used by the mobile station UE for periodically transmitting a CQI used for the AMC and the like of the mobile station UE.
The “resources for a PUCCH-SR” are resources used by the mobile station UE for transmitting the SR.
A method including extending a cycle to allocate the individual resources (a first method), a method including increasing the number of mobile stations UE to be multiplexed in one subframe (a second method), and the like are generally thought of as methods to solve the above-described problem of the “always-on” method.